B520A BOX, CEILING W/NAIL | With captive nails. 3/0 - 4/0 combination. Fixture spacing for 2-3/4 to 3 in, six integral clamps. 4 in Dia non-metallic ceiling box, 20 cu-in volume. Listed for fixture support up to 50 lb. 4 in Dia x 2-1/4 in D. Meets NEMA OS-2, UL listed and RoHS compliance.